Two-cycle internal combustion engine with pump means

ABSTRACT

A multiple cylinder, two-stroke cycle, internal combustion engine is provided which includes a rotary pump that uninterruptedly introduces a pressurized mixture of fuel and air into an undivided crankcase common to all cylinders and maintains the mixture under pressure while in the crankcase. The pump is an integral part of the engine block assembly and a passageway therein provides direct communication between a chamber of the pump and the crankcase. In addition to a conventional exhaust outlet port, the constant pressurization of the fuel mixture in the crankcase avoids the need to compartmentalize the crankcase in accordance with the number of cylinders and also avoids the need to provide fuel inlet valves to the crankcase as has been heretofore required by two-cycle engines having more than one cylinder.

United States Patent [191 Shelton 1 Sept. 9, 1975 1 1 TWO-CYCLE INTERNAL COMBUSTION [73] Assignee: Industrial Research Company,

Kansas City, Mo.

[22] Filed: Jan. 24, I974 [21] Appl. No.: 436,137

Prinuzry E.mminerCharles J. Myhre Assistant Exuminer-William C. Anderson Attorney, Agent, or Firm-Schmidt, Johnson, l-lovey & Williams 57] ABSTRACT A multiple cylinder, two-stroke cycle, internal combustion engine is provided which includes a rotary pump that uninterruptedly introduces a pressurized mixture of fuel and air into an undivided crankcase common to all cylinders and maintains the mixture under pressure while in the crankcase. The pump is an integral part of the engine block assembly and a passageway therein provides direct communication between a chamber of the pump and the crankcase In addition to a conventional exhaust outlet port, the constant pressurization of the fuel mixture in the crankcase avoids the need to compartmentalize the crankcase in accordance with the number of cylinders and also avoids the need to provide fuel inlet valves to the crankcase as has been heretofore required by twocycle engines having more than one cylinder.

2 Claims, 7 Drawing Figures TWO-CYCLE INTERNAL COMBUSTION ENGINE WITH PUMP MEANS This invention relates to a two-stroke cycle, multiple cylinder, internal combustion engine commonly referred to as a two-cycle engine.

conventionally, two-cycle engines are characterized by their simplicity in that ports are used for introducing fuel into the cylinders and for exhausting the gases rather than some type of mechanically operated valve mechanism which is typical of the four-stroke cycle engines. The matter of relying on crankcase compression, caused by the action of the pistons, to force fuel into the cylinders is complicated in multiple cylinder, twostroke engines because of the heretofore need to compartmentalize the crankcase into airtight sections so that compression for each cylinder could occur as its respective piston reciprocates. One of the problems caused by this compartmentalization is that of furnishing a constant and even supply of fuel to all of the cylinders from a single carburetor. Attempts have been made to solve this problem by providing special valve means between the crankcase sections which, of course, partially defeats the basic advantage of twocycle engines over four-cycle engines, that being their simplicity which is made possible by the elimination of valve mechanisms.

Also, since the ports of the cylinders are open only a relatively short time, the two-cycle engine is usually less suitable for high-speed purposes than the fourcycle engine. It is possible to modify two-cycle engines to obtain a greater speed, but this again requires the need for auxiliary exhaust valves, mechanically operated, to aid in clearing the cylinder of the burned gases and to indirectly aid in obtaining a better induction of a fresh charge of fuel from the crankcase. Here again, part of the advantage of the two-cycle engine is again lost because of the need for mechanically operated valves.

It is, therefore, a very important object of my invention to provide a multiple-cylinder, internal combustion engine of the two-stroke cycle type which does not require compartmentalization of the crankcase or provision of any type of valve means either for the introduction of fuel into the crankcase, or to aid in the scavenging and recharging of the cylinders.

It is a further very important object of my invention to provide a two-cycle engine which is capable of providing a given horsepower at an appreciably lower rpm than that heretofore obtainable.

Yet another significant object of the instant invention is to provide a two-cycle engine in which the fuel pressure in the crankcase is maintained at a substantially constant rate, regardless of the relative dispositions of the respective pistons in their cylinders, and at a substantially lower rate of pressure than has been conventionally thought to be necessary.

A still further object of the present invention is to provide a two-cycle engine having an integral blowerscavenger which pressurizes the crankcase as well as aids in the exhaust scavenging of the cylinders.

A yet further object of the invention is to provide a two-cycle engine having an integral blower-scavenger which may be incorporated for use with engines of various piston and cylinder configurations, such as radial, in-line, V, and opposed.

Another object of the present invention is to provide a two-cycle engine in which the tendency for fuel to be sucked out of the cylinder and back into the crankcase when the piston is in its cylinder compression stroke is eliminated.

In the drawings:

FIG. 1 is a plan view of an internal combustion engine made pursuant to the present invention and depicting a radial-type engine as may be used in connection with aircraft;

FIG. 2 is an enlarged, end elevational view illustrating that end of the engine at which the mounting and flywheel are normally disposed, with the flywheel removed and a portion of the engine mounting broken away;

FIG. 3 is a cross-sectional view taken along irregular line 33 of FIG. 2;

FIG. 4 is a fragmentary, cross-sectional view taken along line 44 of FIG. 2;

FIG. 5 is a fragmentary, cross-sectional view taken along line 55 of FIG. 3;

FIG. 6 is a fragmentary, cross-sectional view taken along line 66 of FIG. 5; and

FIG. 7 is a fragmentary, cross-sectional view taken along irregular line 77 of FIG. 5.

A two-stroke cycle, multiple cylinder, internal combustion engine, broadly designated by the numeral 10, is comprised, in its preferred embodiment, of a block assembly 12 presenting a plurality of radially arranged cylinders 14, an undivided crankcase 16, a piston unit 18 for each cylinder, a crankshaft 20 disposed in the crankcase 16 and operably coupled with the pistons 18, and a rotary pump, broadly designated by the numeral 22, integral with the block assembly 12.

The radial piston configuration presented by the block assembly 12 is similar to that conventionally used in connection with light aircraft and the like, and the crankcase 16 is defined by a central, generally cubeshaped, hollow case portion 24 having opposed sidewalls 26 each' provided with circular openings 28 and to which respective cylinder heads 30 are removably attached such that the cylinders 14 are in communication with the crankcase 16 through the openings 28. The crankcase 16 is further defined by a wall 32 at that end of the block assembly 12 normally referred to as the flywheel end, and an opposite partition wall 34 integral to both the case 24 and the pump 22.

The cylinder heads 30 are of conventional construction as is well known and understood in the manufacture of air-cooled, radial-type engines and a cylindrically-shaped wall 38 of each head 30 includes the usual fuel bypass 36 which leads from the crankcase 16 to a fuel inlet port 40 of the-cylinder 14. Accordingly, a conventional exhaust outletport 42 is provided in the wall 38 opposite the inlet port 40.

The pump means 22, which is an integral part of the block assembly 12, is of the rotary piston type and includes a casing 44 which, together with the case portion 24, generally defines the block assembly 12 and presents a cylindrical chamber 46 which receives a specially formed piston or rotor 48 that is keyed to an extension 50 of the crankshaft 20 for rotation therewith. Except for minor structural modification to adapt it to the case portion 24, the pump 22 is, for all practical purposes, the same as that disclosed in my US. Pat. No. 2,948,230, issued Aug. 9, 1960, and entitled Fluid Pump.

As constructed for use in connection with the engine 10, the casing 44 is medially split to present a pair of similar sections 52 and 54, releasably held together by a plurality of fasteners (not shown). The casing 44 with its chamber 46, presents a pair of interior, opposed, flat, circular walls 56 and 58 and an annular wall 60 spanning the distance transversely thereof between the walls 56 and 58.

The rotor or piston 48 is somewhat in the nature of a conventional swash plate in that it is set on a circular hub 62 obliquely of the latter as best seen in FIGS. 3 and 5. The hub 62 is provided with a pair of opposed, flat, circular faces 64 and 66 which bear flatly against annular seals 68 affixed to the circular walls 56 and 58, it being understood that the piston 48 is an integral part of the rotatable hub 62.

The axis of rotation of the hub 62 and therefore the piston 48, is concentric with the wall 60 with the crankshaft 20 being carried by a plurality of bearings 70 which are, in turn, carried by the walls 32 and 34 of the case portion 24 and the section 52 of the casing 44. It will thus be seen that the crankshaft 20 and the piston 48 are axially aligned along a common axis and rotate simultaneously with each other. A bearing seal 72 is provided for each of the bearings 70 carried by the end wall 32 and the section 52.

An integral boss 74 extends radially from the casing 44 and is provided with a flat, substantially rectangular face 76 to which is attached a cover plate 78 along with proper gasket sealing material 80. An elongated slot 82 within the, boss 74 extending throughout the length of the casing 44 from end-to-end thereof and transversely radial to the chamber 46, extends through the latter or traverses the chamber 46, as best seen in FIG. 5, and is therefore also formed in the walls 56 and 58. The slot 82 terminates at its innermost edge 84 flush with the cylindrical face of the hub 62 and is, therefore, radial to the latter for receiving a reeiprocable partition broadly designated by the numeral 86, the innermost longitudinal edge of the partition 86 sliding along the wall which forms the innermost edge 84 of the slot 82. It is to be noted that the plate 78 covers the slot 82 and, therefore, slidably receives the outermost longitudinal edge ofthe reeiprocable partition 86. The boss 74 is provided with opposed end pieces 88 and 90 which close the opposed lateral ends of the slot 82; thus it will be seen that no portion of the slot 82 is exposed.

A mixture of fuel and air, supplied by a carburetor 92 of any readily available type compatible for use with a two-cycle engine, is directed into the chamber 46 by means of an intake port 94 extending inwardly from the face 76 and through the wall 58. It is to be understood that the carburetor 92 is suitably affixed to the plate 78; thus the port 94 places the carburetor in direct communication with the chamber 46. Similarly, an exhaust port 96 extends inwardly from the face 76 and communicates with the chamber 46 through wall 58 in relative close proximity to the slot 82 and, therefore, partition 86 on opposite sides of the latter. Attention is directed to FIGS. 3 and wherein it is shown that an elongated bore 97 in the boss 74 longitudinally intersects the port 96, is of a somewhat greater diameter than that of the port 96, and terminates at its inner end 98 (FIG. 3) in a passage 100, through the wall 34, which leads directly into the crankcase 16.

In the same manner, the section 52 of the casing 44 is provided with an inlet port 102 that extends inwardly from the face 76 communicating with the chamber 46 through wall 56, and an exhaust port 104 extending inwardly from the face 76 communicates with the chamber 46 to the wall 56. The ports 102 and 104 are disposed on opposite sides of the partition 86 and are directly opposed to the ports 94 and 96 respectively of the wall 58.

The plate 78 covers the ports 96, 102, 104 and bore 97, but is provided with an opening 106 (FIG. 4) that communicates with the port 94 and the carburetor 92. Ports 94 and 102 are interconnected by a passage 108 in the boss 74, and a passage 110 interconnects the ports 96 and 104.

Based upon the foregoing, it is now apparent that the fuel and air mixture flows from the carburetor 92 into the chamber 46 by way of the port 94, and also from port 94, through the passage 108 and thence through the port 102 into the chamber 46. The fuel and air mixture is exhausted from the chamber through port 96 and bore 97 to the passage and thence to the crankcase l6 and is also exhausted from the chamber 46 through the port 104 to the passage and thence to the crankcase 16 by way of the port 96, bore 97 and passage 100.

As hereinabove indicated, the piston 48 is somewhat in the form of a swash plate in that it is set obliquely on the hub 62 and, therefore, spans the distance between the walls 56 and 58, and has a special configuration in that its purpose is to pump the fuel and air mixture from carburetor 92 to the crankcase 16 rather than for the primary purpose of reciprocating a driven element as in the case of a conventional swash plate.

It is to be noted initially that the circular periphery 112 of the piston 48 is transversely parallel to the axis of rotation of the crankshaft 20 and is disposed in close proximity to the annular wall 60 of the chamber 46 so that at no time is any of the fuel and air mixture permitted to pass from one side of the piston 48 in chamber 46 to the opposite side thereof. Additionally, it is important to note that both of the opposed faces 1 14 and 116 of the piston 48 are radially perpendicular throughout their circumferential lengths, are perpendicular to the outermost annular face of the hub 62, perpendicular to the annular wall 60, and therefore to the axis of rotation of the crankshaft 20, hub 62 and piston 48. By virtue of such relationship of the faces 114 and 1 16 to the axis of rotation, and by virtue of the fact further, that the piston 48 is of uniform thickness throughout, each face 116 and 114 is substantially concave throughout approximately half its circumferential length and substantially convex throughout approximately the remaining half of its circumferential length. Thus, the concave portion of face 114 is opposite the convex portion of the face 116 and vice versa.

Manifestly, on each face 114 and 116, the concave portions merge gradually and progressively with the convex portions to the end that at all times within the chamber 46, there is presented a compartment of progressively decreased dimensions as the faces 64 and 66 are approached in both directions circumferentially of the annular face of the hub 62. Thus, there are what may be termed residual ridges or portions which are in substantial line contact with the walls 56 and 58 and ex tend radially outwardly from the hub 62 and in perpendicular relationship to the latter and to the annular wall 60. In FIG. 3, the numeral 118 represents the ridge or portion of the face 114 which is in line contact with the wall 56 and it is to be noted that further in FIG. 3, line 118 is flush with the face 64 of the hub 62. Likewise,

the numeral 120, again in FIG. 3. represents the ridge or portion of faee'114that is in line'contact with wall 58, this portion also being flush with the corresponding face 66 of the hub 62. It is to be further noted that the line contact of the portion 118 of face 116 is necessarily directly opposite the deepest area of the concave portion of the face 114.

By virtue of the-fact that the faces 114 and 116' are transversely radial to the hub 62 and wall 60 throughout the lengths thereof, the piston 48 is adapted to be received by a transverse slot 122 extending inwardly into the partition 86 midway between the ends thereof and from its innermost longitudinal edge,the length of the slot 122 being substantially the same as thewidth of the piston 48. It is to be noted iii FIG. 5 that the par-.

tition 86 is beveled in oppositedirections throughout the length of the slot 122 to present relatively short, elongated edges 124 and 126which are in substantial line contact with the faces 114 and 116 of the piston It is to be noted that the crankshaft 20 is of the standard single-throw type having the usual counterweights 128 and a radially offset crankpin 130 to which a connecting rod 132 is releasably attached for each of the piston units 18.It is to be here further n otedthat the piston units 18 may be of any conventional construction with their respective connecting rods 132 being suitably attached to the crankpin 130 ina side-by-side manner longitudinally therealong. In viewing FIGQ3, it is observed however, that only two of the four connecting rods are shown, it being understood that the other two connecting rods for the four-cylinder engine would be properly disposed in the remaining areas of the pin 130. In this connection it is to be seen in viewing FIG. 1 that the cylinders 14, as defined by the cylinder heads 30, are offset relative to one another longitudinally of the crankshaft 20. I I

Additionally, note is to be made of the fact that the single-piece crankshaft 20 not only serves the piston units 18 to cause their reciprocable movements in the cylinders 14, but also provides the mounting for thepiston 48 and its hub 62 as well as furtherhaving a forward extension 134 which may be used as a power takeoff such as for the attachment of a. propeller when the engine is used in connection with anaircraft.

A suitable mounting structure 136 is provided at the normally rearwardmost end of ,the engine adjacent the end wall 32 of the case 24 and provision may be made on such structure for the carrying of various auxiliary engine attachments such as a starter motor (-not shown) for use in connection with a flywheel 138 keyed to an end 140 of the crankshaft 20 opposite the extension 134 and suitably secured as bysa nut 135. Flywheel 138 may also have provision for driving an ignition distribu-' tor 142" which is carried to vthe mounting 136 and driven by a belt and pulley arrangement 144. A wiring harness 148 leads from the distributor 142 to interconnect the latter with a spark plug 146 at each cylinder head 30.

Suitable fittings 150 are provided at each cylinder head 30 in connection with its exhaust outlet port 42 to lead the exhaust away from the cylinder to a suitable manifold or muffler device (not shown) if desired. Mention is made that the engine" is provided with all of the usual gaskets'and other sealing devices needed for the normal operation of an internal combustion en- 152 in each cylinto traverse the intake port 102;of .wall 56 as seen in FIG. 5. As the line 118 moves away from the partition 86, the space within the chamber 46, between the line 118 and the partition 86 and between the concavity-of the face 116 and the wall 56 progressively increases in volume thereby drawing the fuel and air mixture thereinto from the intake port 102. 7

By the time the line 118 has rotated from the position shown in FIG. 5 to the end of its intake stroke again in alignment with partition 86, the concavity of the face 116 will have been completely filled with the fuel and air mixture and such will be carried circumferentially around the wall to the exhaust port 104 as soon as -the line 118 traverses the inlet 102.

Consequently, at all times the face 116 is effective in drawing fluid into the chamber 46 while it simultaneously forces the mixture therefrom. The mixture contained in its concavity is confined between the portion or line 118 and the partition 86,-T,hu s, when the concavity of the face 1 16 commences to communicate with the intake port 102, i.e.,as the line 118 moves from the partition 86 to the port 102, such c oncavity will have been exhausted of the fuel and. air mixture and the resultant reduced pressure thereincauses the mixture to flow from the carburetor 92, through the passage 108 and into the chamber 46 between the face 116' and wall 56 via the intake port 102.

': The intake and exhaust strokes of the face 114 of th piston 48 operate in the same manner and need not be repeated, except to point out that the operation of the ,faces 114, 116 are in converse relationship. In other words, as the face 116 commences-its intake stroke, face 114 is approaching the completion of its intake stroke and therefore, fluid mixture flows simultaneously into both sections of the chamber 46 on opposite sides of the piston 48 virtually-without interruption, except only for the extreme small interval .of time during which line portion 118 moves from partition'86-to intake port 102, and line portion 120 moves from the partition 86 to the intake port 94. Conversely, fuel mixture flows continuous-1y from both sections of the chamber 46 except only for the small interval of time during which the lines 118 and 120 move from their outlet ports 96 and 104 respectively to and across the partition 86. Accordingly, there is a continuous, non-pulsating, even flow of the fuel and air mixture through the pump 22 with virtually no change in volume, pressure or velocity during continuous rotation of the piston 48 within the chamber 46.

course, it is to-be further pointed out that the cross-passages 108 and interconnecting the inlet ports 94 and 102 and. 96 and 104 respectively, results in there being equalquantities of fuel in the chamber 46 at equal'pressures, on either side of the piston 48. Further, there is a virtually continuous supply of the fuel mixture being introduced into the crankcase 16 by virtue of the direct communication (there being no valves) between the crankcase and the discharge or exhaust port 96 as is best seen in FIG. 3.

The continuous induction and forcing of fuel and air into the crankcase 16 by the pump 22 is attributable not only to the shape and configuration of the piston 48 but to the disposition and the way in which the partition 86 is reciprocably actuated by the piston 48 transversely of the chamber 46 and within the boss 74 to maintain a constant line of division extending from the wall 60 to the hub 62 where the innermost longitudinal edge of the partition 86 slidably engages the hub as the latter rotates and as the partition 86 reciprocates along a path of travel in alignment with the axis of the crankshaft 20.

Thus, it will be seen that the crankcase 16 is continu ously pressurized at a substantially constant pressure such that reliance need not be made on the reciprocable action of the pistons 18 for compressing of the fuel in the crankcase and forcing the fuel through the bypass 36 into the cylinder 14 of each cylinder head 30. Therefore, the need for a compartmentalized crankcase or for special fuel induction valves has been eliminated and the simplicity of a conventional two-stroke cycle engine has been retained in connection with a multiple cylinder, two-stroke engine.

The blower-scavenger nature of the pump 22 is best illustrated when it is understood that fuel is forced directly into a particular cylinder 14 when its piston 18 is at the end of its power stroke, leaving the cylinder 14 in direct communication with the pump rotor 48 via the outlet ports 96 and 104, passage 100, crankcase l6 and bypass 36 as the piston clears the port 40. Therefore, fuel flows from the crankcase without the use of valves into the cylinder because of the pressure created by the pump and the incoming fuel, under pressure, pushes the exhaust gases out the exhaust port 42 to scavenge the cylinder. Of course, as each piston proceeds along its compression stroke, it will close its respective ports 40 and 42. In this connection, the ports are slightly offset with respect to each other longitudinally along the cylinder so that the piston clears the exhaust port 42 before clearing the inlet port 40 when on its power stroke and closes the inlet port 40 before the exhaust port 42 when on its compression stroke. Thus, the exhaust port 42 is open a slightly longer period of time to permit adequate time for the exhaust gases to escape.

Conventional two-cycle engines operate at a pressure of 12-20 psi in the crankcase and there is a pressure drop when the piston is at the top of the stroke, whereas it has been found that in the engine of the instant invention a pressure of 9 psi in the crankcase is adequate and, additionally, the pressure is constant, regardless of the relative positions of the respective pistons.

The efficiency of this novel engine is further exemplified in that it has been determined that a 65 cubic inch, four-cylinder engine will develop approximately 65 horsepower at 4400-4500 rpm, whereas conventional two-cycle engines must operate at approximately 6500 rpm to get one horsepower/cubic inch. A further advantage then becomes readily apparent in that the life expectancy of the engine is increased because of the approximate one-third reduction in rpm.

It is to be understood of course, that the capacity of the pump 22 may be varied to meet the requirements of the size engine of which it is a part and it may be easily modified, depending on the requirements of the engine. The distance between the walls 56 and 58, the thickness of the piston 48, the diameter of the hub 62, and the diameter of the wall 60 are all variable and such changes have a direct bearing on the capabilities of the pump.

Whereas other types of pumps might be adapted for use in connection with the engine as herein disclosed, it has been found that this pump is most desirable in that it is designed to eliminate all necessity for any type of valving; thus, the only moving parts, as far as the pump is concerned, are the piston 48 itself and the vane 86.

Additionally, this pump 22 is most readily adaptable for use with the instant engine in that it can be integrally made a part of the engine and it is therefore the most practical. Because the pump 22 is of such a configuration that it can be an integral part of the engine, it will be further seen that the rotor or piston 48 may be mounted directly to the crankshaft 20 for unitary rotation therewith which further typifies the simplicity of the engine and is an important factor as far as weight is concerned. The weight of the aforementioned horsepower engine fromflywheel to blower with no accessories is approximately pounds and is therefore very adaptable for use in connection with aircraft and the like.

Whereas the preferred embodiment of this novel engine has been illustrated and described, it is to be further understood that other forms of the invention may be made without departing from the true spirit of the invention and the fair scope of the claims. For example, it may be desirable, in certain instances, to introduce the fuel and air mixture directly into the cylinders via a manifold-type arrangement interconnecting the pump with the various fuel inlets rather than through the crankcase as described. The advantage in this case would be that the need to premix the fuel and lubricating oil for the engine, as is typical with two-cycle en'- gines, would be avoided and an unmixed fuel could thus be used through the carburetor.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

l. A two-cycle internal combustion engine comprising in combination:

a block assembly presenting a plurality of cylinders and an undivided crankcase common to all cylinders;

a piston unit for each cylinder;

a crankshaft disposed in said crankcase and operably coupled with said pistons;

each cylinder being provided with a fuel inlet and an exhaust outlet;

said block assembly further including a positive displacement pump means integral therewith,

said pump means having a pressure chamber separate from said crankcase and including a rotary piston in said chamber coupled to said crankshaft for rotation about a common axis therewith,

said chamber being in continuous flow communication with the fuel inlet of each cylinder;

means for providing a premixed fuel and air supply to said pump means whereupon said mixture is pressurized in said chamber and uninterruptedly supplied to each inlet under substantially uniform pressure; and

means for combusting said mixture when admitted into said cylinders through said inlets.

2. An engine as set forth in claim 1 wherein said fuel a substantially constantly uniform supply of pressurized inlets are in direct communication with said crankcase. fuel and air is provided to each fuel inlet from said said pressure chamber of said pump means also being pump chumbervia said crankcase. in direct communication with said crankcase whereby 

1. A two-cycle internal combustion engine comprising in combination: a Block assembly presenting a plurality of cylinders and an undivided crankcase common to all cylinders; a piston unit for each cylinder; a crankshaft disposed in said crankcase and operably coupled with said pistons; each cylinder being provided with a fuel inlet and an exhaust outlet; said block assembly further including a positive displacement pump means integral therewith, said pump means having a pressure chamber separate from said crankcase and including a rotary piston in said chamber coupled to said crankshaft for rotation about a common axis therewith, said chamber being in continuous flow communication with the fuel inlet of each cylinder; means for providing a premixed fuel and air supply to said pump means whereupon said mixture is pressurized in said chamber and uninterruptedly supplied to each inlet under substantially uniform pressure; and means for combusting said mixture when admitted into said cylinders through said inlets.
 2. An engine as set forth in claim 1 wherein said fuel inlets are in direct communication with said crankcase, said pressure chamber of said pump means also being in direct communication with said crankcase whereby a substantially constantly uniform supply of pressurized fuel and air is provided to each fuel inlet from said pump chamber via said crankcase. 